1. Field of Invention
The present invention relates to a data recovery device and a data recovery method. More particularly, the present invention relates to a data recovery device and a data recovery method that can be used in an optical storage system.
2. Description of Related Art
Common optical storage systems use laser discs, such as compact discs (CDs) and digital versatile discs (DVDs). To reproduce data stored in an optical disc, an optical disc drive (ODD) projects a laser beam onto the surface of the optical disc. The ODD then reads the laser beam reflected from the optical disc. An electric signal generated according to the reflected laser beam is a radio frequency (RF) signal. There are many reasons that may cause distortion on the RF signal, such as the non-linear channel used during de-focusing, inter-symbol interference (ISI), electrical delay, the pit patterns on the optical disc generated through mass production or injection molding, the scratches on the surface of the disc, aging of the disc, and so on. Distortion leads to decrease in the quality of the RF signal and deterioration of the recognition performance of the ODD. When the ODD reads the optical disc at a high speed, the ISI problem becomes even more severe.
To maintain the transmission speed and signal quality at the same time, a partial response (PR) method is usually applied to the conventional optical storage systems to allow ISI within a certain extent. Specifically, the PR method calibrates errors in the signal levels to obtain digital data upon which data can be processed. The Viterbi decoding mechanism of the maximum likelihood (ML) method can be applied to decode the resulting digital data into the originally stored data. Theoretically, the Viterbi decoding mechanism can minimize the errors. However, the mechanism is extremely complicated and difficult to implement. For example, FIG. 1 shows a frequency response waveform diagram of a read channel according to the related art. In a practical optical storage system, the frequency response Ch_1 of the real read channel is similar to neither the partial response channel PR1 nor the partial response channel PR2. If either the partial response channel PR1 or the partial response channel PR2 is used for reading purposes, there will be severe errors. Relatively speaking, if the partial response channel PR3 is used for reading purposes, there will be fewer errors. However, implementing a similar partial response channel will not only incur much additional costs but also complicate circuit designs. In fact, it is relatively simple to implement a less similar partial response channel. Therefore, researches are made as to use a less similar partial response channel for reading purposes and to compensate for the frequency response of the real read channel.